A variety of new secondary electrochemical cells that exhibit high energy density have been demonstrated. However, commercial systems remain primarily based on lithium ion (Li-ion) chemistry. Such cells frequently consist of a layered transition metal oxide cathode material, an anode-active lithium metal or lithium intercalation or alloy compound such as graphitic carbon, tin and silicon, and an electrolytic solution containing a dissolved lithium-based salt in an aprotic organic or inorganic solvent or polymer. Today there is great demand for energy storage devices that exhibit higher volumetric and gravimetric energy density when compared to commercially available lithium ion batteries. Consequently an increasingly sought after route to meeting this demand higher energy density is to replace the monovalent cation lithium (Li+) with multi-valent ions, such as divalent magnesium cations (Mg2+), because these ions can enable many times the charge of Li+ to be transferred per ion.
Furthermore, alkali metals, and lithium in particular, have numerous disadvantages. Alkali metals are expensive. Alkali metals are highly reactive. Alkali metals are also highly flammable, and fire resulting from the reaction of alkali metals with oxygen, water or other active materials is extremely difficult to extinguish. Lithium is poisonous and compounds thereof are known for their severe physiological effects, even in minute quantities. As a result, the use of alkali metals requires specialized facilities, such as dry rooms, specialized equipment and specialized procedures.
Gregory et al., “Nonaqueous Electrochemistry of Magnesium; Applications to Energy Storage” J. Electrochem. Soc., Vol. 137, No. 3, March 1990 discloses Co3O4, Mn2O3, Mn3O4, MoO3, PbO2, Pb3O4, RuO2, V2O5, WO3, TiS2, VS2, ZrS2, MoB2, TiB2, and ZrB2 as positive electrode materials for a magnesium battery. However, only the first cycle discharge is shown and all materials exhibit significant polarization for medium current densities.
Novak et al., “Electrochemical Insertion of Magnesium in Metal Oxides and Sulfides from Aprotic Electrolytes,” JECS 140 (1) 1993 discloses TiS2, ZrS2, RuO2, Co3O4 and V2O5 as positive electrode materials of a magnesium battery. However, only layered V2O5 shows promising capacity and reversibility. Furthermore, Novak et al. show that Mg2+ insertion into this oxide depends on the ratio between the amounts of H2O and Mg2+ as well as on the absolute amount of H2O in the electrolyte. According to Novak, water molecules preferentially solvate Mg2+ ions, which facilitate the insertion process by co-intercalation.
Novak et al., “Electrochemical Insertion of Magnesium into Hydrated Vanadium Bronzes”Electrochem. Soc., Vol. 142, No. 8, 1995 discloses Mg2+ insertion into layered vanadium bronzes, MeV3O8(H2O)y where (Me=Li, Na, K, Ca0.5, and Mg0.5). Variations in the content of bound lattice water in the bronzes were found to be responsible for a difference in the electrochemical properties of the same starting material dried at different temperatures. The presence of this water was deemed essential but the lattice water is removed during cycling after which the capacity deteriorates. Furthermore, attempts to cycle the compounds in dry electrolytes failed. The beneficial effect of water was speculated to be due to its solvation of the Mg2+ ion.
Le et al., “Intercalation of Polyvalent Cations into V2O5 Aerogels” Chem. Mater. 1998, 10, 682-684 discloses multi-valent ion insertion into V2O5 areogels where the small diffusion distances and high surface area are regarded as beneficial for multi-valent intercalation. X-ray diffraction of the aerogel shows an interlayer spacing of 12.5 A (due to retaining acetone), as compared to the 8.8 A characteristic of the V2O5*0.5H2O xerogel.
Amatucci et al., “Investigation of Yttrium and Polyvalent Ion Intercalation into Nanocrystalline Vanadium Oxide,” J Electrochem Soc, 148(8), A940-A950, Jul. 13, 2001, show reversible intercalation of several multi-valent cations (Mg2+, Ca2++, Y3+) into nano-metric layered V2O5 but with significant polarization (e.g., energy loss) and at a low rate of 0.04 C which signifies the low diffusivity of the Mg ions.
The current, proven state of the art high energy, rechargeable Mg cell is described by Aurbach et al., U.S. Pat. No. 6,316,141, issued Nov. 13, 2001, as a cell comprised of a magnesium metal anode, a “Chevrel” phase active material cathode, and an electrolyte solution derived from an organometallic complex containing Mg. Chevrel compounds are a series of ternary molybdenum chalcogenide compounds first reported by R. Chevrel, M. Sergent, and J. Prigent in J. Solid State Chem. 3, 515-519 (1971). The Chevrel compounds have the general formula MxMo6X8, where M represents any one of a number of metallic elements throughout the periodic table; x has values between 1 and 4, depending on the M element; and X is a chalcogen (sulfur, selenium or tellurium). Furthermore, in E. Levi et al, “New Insight on the Unusually High Ionic Mobility in Chevrel Phases,” Chem Mat 21 (7), 1390-1399, 2009, the Chevrel phases are described as unique materials which allow for a fast and reversible insertion of various cations at room temperature.
Michot et al., U.S. Pat. No. 6,395,367, issued May 28, 2002, is said to disclose ionic compounds in which the anionic load has been delocalized. A compound disclosed by the invention includes an anionic portion combined with at least one cationic portion Mm+ in sufficient numbers to ensure overall electronic neutrality; the compound is further comprised of M as a hydroxonium, a nitrosonium NO+, an ammonium NH4+, a metallic cation with the valence m, an organic cation with the valence m, or an organometallic cation with the valence m. The anionic load is carried by a pentacyclical nucleus of tetrazapentalene derivative bearing electroattractive substituents. The compounds can be used notably for ionic conducting materials, electronic conducting materials, colorant, and the catalysis of various chemical reactions.
U.S. Pat. No. 6,426,164 B1 to Yamaura et al., issued Jul. 30, 2002, is said to disclose a non-aqueous electrolyte battery capable of quickly diffusing magnesium ions and improving cycle operation resistance, incorporating a positive electrode containing LixMO2 (where M is an element containing at least Ni or Co) as a positive-electrode active material thereof; a negative electrode disposed opposite to the positive electrode and containing a negative-electrode active material which permits doping/dedoping magnesium ions: and a non-aqueous electrolyte disposed between the positive electrode and the negative electrode and containing non-aqueous solvent and an electrolyte constituted by magnesium salt, wherein the value of x of LixMO2 satisfies a range 0.1≦x≦0.5. It is also said that for Li concentrations x 0.1, the host material becomes unstable and for higher Li concentrations x≧0.5, there are not enough available Mg lattice sites available. Specifically, there is no mention of interlayer distance.
Michot et al., U.S. Pat. No. 6,841,304, issued Jan. 11, 2005, is said to disclose novel ionic compounds with low melting point whereof the onium type cation having at least a heteroatom such as N, O, S or P bearing the positive charge and whereof the anion includes, wholly or partially, at least an ion imidide such as (FX1 O)N− (OX2 F) wherein X1 and X2 are identical or different and comprise SO or PF, and their use as solvent in electrochemical devices. Said composition comprises a salt wherein the anionic charge is delocalised, and can be used, inter alia, as electrolyte.
U.S. Patent Application Publication No. 20090068568 A1 (Yamamoto et al. inventors), published on Mar. 12, 2009, is said to disclose a magnesium ion containing non-aqueous electrolyte in which magnesium ions and aluminum ions are dissolved in an organic etheric solvent, and which is formed by: adding metal magnesium, a halogenated hydrocarbon RX, an aluminum halide AlY3, and a quaternary ammonium salt R1R2R3R4N+Z− to an organic etheric solvent; and applying a heating treatment while stirring them (in the general formula RX representing the halogenated hydrocarbon, R is an alkyl group or an aryl group, X is chlorine, bromine, or iodine, in the general formula AlY3 representing the aluminum halide, Y is chlorine, bromine, or iodine, in the general formula R1R2R3R4N+Z− representing the quaternary ammonium salt, R1, R2, R3, and R4 represent each an alkyl group or an aryl group, and Z− represents chloride ion, bromide ion, iodide ion, acetate ion, perchlorate ion, tetrafluoro borate ion, hexafluoro phosphate ion, hexafluoro arsenate ion, perfluoroalkyl sulfonate ion, or perfluoroalkyl sulfonylimide ion. These additives are aimed at increasing the stability of the electrolyte in atmospheric air and facilitate the production process for said electrolytes.
U.S. Patent Application Publication No. 20100136438 A1 (Nakayama et al. inventors), published Jun. 3, 2010, is said to disclose a magnesium battery that is constituted of a negative electrode, a positive electrode and an electrolyte. The negative electrode is formed of metallic magnesium and can also be formed of an alloy. The positive electrode is composed of a positive electrode active material, for example, a metal oxide, graphite fluoride ((CF)n) or the like, etc. The electrolytic solution is, for example, a magnesium ion containing nonaqueous electrolytic solution prepared by dissolving magnesium(II) chloride (MgCl2) and dimethylaluminum chloride ((CH3)2AlCl) in tetrahydrofuran (THF). In the case of dissolving and depositing magnesium by using this electrolytic solution, they indicate that the following reaction proceeds in the normal direction or reverse direction.
According to this, there are provided a magnesium ion-containing nonaqueous electrolytic solution having a high oxidation potential and capable of sufficiently bringing out excellent characteristics of metallic magnesium as a negative electrode active material and a method for manufacturing the same, and an electrochemical device with high performances using this electrolytic solution.
U.S. Patent Application Publication No. 20110111286 A1 (Yamamoto el at. inventors), published on May 12, 2011, is said to disclose a nonaqueous electrolytic solution containing magnesium ions which shows excellent electrochemical characteristics and which can be manufactured in a general manufacturing environment such as a dry room, and an electrochemical device using the same are provided. A Mg battery has a positive-electrode can, a positive-electrode pellet made of a positive-electrode active material or the like, a positive electrode composed of a metallic net supporting body, a negative-electrode cup, a negative electrode made of a negative-electrode active material, and a separator impregnated with an electrolytic solution and disposed between the positive-electrode pellet and the negative-electrode active material. Metal Mg, an alkyl trifluoromethanesulfonate, a quaternary ammonium salt or/and a 1,3-alkylmethylimidazolium salt, more preferably, an aluminum halide are added to an ether system organic solvent and are then heated, and thereafter, more preferably, a trifluoroboraneether complex salt is added thereto, thereby preparing the electrolytic solution. By adopting a structure that copper contacts the positive-electrode active material, the electrochemical device can be given a large discharge capacity.
Nazar et al, “Insertion of Poly(p-phenylenevinylene) in Layered MoO3”, J. Am. Chem. Soc. 1992, 114, 6239-6240 discloses insertion of high molecular weight PPV into a layered oxide by intercalating the PPV precursor polymer between the layers of MoO3, by ion exchange. The layer spacing was reported to increase from 6.9 Å to 13.3 Å. No electrochemical investigations of the host material were performed.
Nazar et al, “Hydrothermal Synthesis and Crystal Structure of a Novel Layered Vanadate with 1,4-Diazabicyclo[2.2.2]octane as the Structure-Directing Agent: C6H14N2—V6O14.H2O” Chem. Mater. 1996, 8, 327 discloses Li insertion into organic cation (C6H12N2 or ‘DABCO’)—templated vanadium oxide resulting from hydrothermal synthesis. The host crystal structure possesses a structure composed of a new arrangement of edge-shared VO5 square pyramids that are corner-shared with VO4 tetrahedra to form highly puckered layers, between which the DABCO cations are sandwiched. The results show that Li insertion is hindered in the DABCO-filled host and improved performance is obtained when the DABCO ion is removed.
Goward et al, “Poly(pyrrole) and poly(thiophene)/vanadium oxide interleaved nanocomposites: positive electrodes for lithium batteries”, Electrochimica Acta, 43, 10-11, pp. 1307, 1998 reports on synthesis and electrochemical investigation of conductive polymer-V2O5 nanocomposites that have a structure comprised of layers of polymer chains interleaved with inorganic oxide lamellae. It was found that for modified [PANI]-V2O5, polymer incorporation resulted in better reversibility, and increased Li capacity in the nanocomposite compared to the original V2O5 xerogel. For PPY and PTH nanocomposites, the electrochemical response was highly dependent on the preparation method, nature of the polymer, and its location. In conclusion, Goward et al note that the results, though promising, were still short of theoretical expectations.
Chirayil et al, ‘Synthesis and characterization of a new vanadium oxide, TMA-V8O20’ J. Mater. Chem., 1997, 7(11), 2193-2195 discloses synthesis of a layered vanadium oxide with a new monoclinic structure in which the tetramethylammonium ions reside between the vanadium oxide layers. The powder X-ray diffraction pattern indicate that this new vanadium oxide has an interlayer spacing of 11.5 Angstrom. Electrochemical investigation of the compound indicates that Li insertion is hindered due to the TMA ions between the layers.
Lutta et al, “Solvothermal synthesis and characterization of a layered pyridinium vanadate, C5H6N—V3O7” J. Mater. Chem., 2003, 13, 1424-1428 reports on synthesis and properties of a layered vanadate which has an aromatic intercalate (pyridinium ion) between the vanadium oxide layers: pyH-V3O7. Chemical lithiation show some reactivity with Li but better performance was obtained when the pyridinium was removed from the vanadate. Indeed, Lutta et al concludes with saying that none of the aromatic V3O7 based structures (TMA-V3O7, MA-V3O7, pyH-V3O7) or their decomposition products lead to electrochemically interesting materials.
The results described above show that slow diffusion of multi-valent ions in layered cathode materials is a limiting factor in rechargeable multi-valent electrochemical cells.
Furthermore, the results above also show that it is commonly believed that organic-inorganic hybrid host materials do not improve intercalation performance, specifically for lithium ions.
There is a need for systems and methods for making improved positive electrode layered materials with high energy density as well as facile Mg ion diffusion.